Wei-Feng Huang

Epitaxial properties of ZnO thin films on SrTiO3 substrates grown by laser molecular beam epitaxy

Epitaxial ZnO thin films with different orientations have been grown by laser molecular beam epitaxy on (001)-, (011)-, and (111)-orientated SrTiO3 single-crystal substrates. The growth behavior was in situ monitored by reflection high-energy electron diffraction, and the epitaxial orientation relations were reconfirmed by ex situ x-ray diffraction measurements. In the case of ZnO on SrTiO3(001), four orthogonal domains coexisted in the ZnO epilayer, i.e., ZnO(110)‖SrTiO3(001) and ZnO[−111]‖SrTiO3⟨100⟩. For (011)- and (111)-orientated substrates, single-domain epitaxy with c axial orientation was observed, in which the in-plane relationship was ZnO[110]‖SrTiO3[110] irrespective of the substrate orientations. Additionally, the crystalline quality of ZnO on SrTiO3(111) was better than that of ZnO on SrTiO3(011) because of the same symmetry between the (111) substrates and (001) films. The obtained results can be attributed to the difference of the in-plane crystallographic symmetry. Furthermore, those align...

GO/PO and PTD With Virtual Divergence Factor for Fast Analysis of Scattering From Concave Complex Targets

Due to simplicity, hybridization of geometrical optics (GO) and physical optics (PO) based on ray tracing has been widely used for fast scattering analyses. However, when targets of curved concavities are discretized by flat facets, the loss of divergence factor (DF) will degrade the simulation accuracy. To remedy this loss, a simple and efficient factor, entitled virtual divergence factor (VDF), is proposed to play the role of DF. To prove the validity of VDF and simulate the scattering of concave complex targets, a hybrid method of GO/PO and physical theory of diffraction (PTD) is elucidated. With VDF correction, several typical targets, including a S-shape cavity, are simulated by this hybrid method. In comparison to multilevel fast multipole algorithm (MLFMA) or measurements, the validaty of VDF is fully demonstrated by good agreements and the excellent performance relative to DF on canonical surfaces, where the great efficiency and flexibility of this hybrid method are also shown. Moreover, one interesting and important issue, the dependance of field convergence on the maximum number of ray reflections, is also investigated for the first time.

Radiation of Arbitrary Magnetic Dipoles in a Cylindrically Layered Anisotropic Medium for Well-Logging Applications

We present a set of stable and efficient formulas to compute the electromagnetic radiation of arbitrary magnetic dipoles in a cylindrically layered anisotropic medium. This set of formulas is derived on the basis of the generalized reflection and transmission coefficients. By expressing our new formulas by the ratios of Bessel or Hankel functions, rather than directly by these special functions, the notorious overflow problem for numerical computation is successfully obviated. Our formulas can be easily implemented for any number of layers, as well as for arbitrary locations and orientations of the transmitter and the receiver. Numerical experiments have demonstrated their correctness and stability. They are then utilized to investigate the influence of the eccentricity distance, the eccentricity angle, and the formation anisotropy on the response of a multicomponent induction logging tool.

Solid-Angle Error in the Magnetic-Field Integral Equation for Perfectly Electric Conducting Objects

For perfectly electric conducting (PEC) objects, one difference between the electric-field integral equation (EFIE) and the magnetic-field integral equation (MFIE) is related to the solid angle, which only exists in the latter. In this communication, the correct computation of solid-angle contribution in MFIE is first summarized and clarified. Through testing strictly inside triangles (TSIT) and testing on edges (TOE) with or without the correct limit value (CLV) for the solid-angle integral, six versions of MFIE are then implemented by utilizing Rao-Wilton-Glisson (RWG) functions for expansion and utilizing RWG or rotated Buffa-Christiansen (BC) functions for testing. Based on the simulations of typical sharp-edged targets and a sphere by the EFIE and six MFIEs, it is found that using CLVs for the solid-angle integral will improve the simulation accuracy substantially in comparison to that with incorrect limit values (ILVs). Moreover, if the singularities are properly handled, the MFIE implemented by TSIT can achieve the same accuracy with the MFIE implemented by TOE with CLVs.

Novel and Stable Formulations for the Response of Horizontal-Coil Eccentric Antennas in a Cylindrically Multilayered Medium

In this paper, we present a set of novel and stable formulations to calculate the response of logging tools with horizontal-coil antennas in an eccentric borehole straddling cylindrically multilayered formations. It can be applied in fast forward computation and the inverse problem for electromagnetic (EM) well-logging in deviated and horizontal wells, where eccentric scenarios are often encountered. Our formulations are different from previous ones in following aspects. First, the tool mandrel can be cylindrically multilayered and the electrical parameters of each layer are arbitrary. Namely, it is not limited to being perfectly metallic. Second, the EM propagation in inhomogeneous medium is considered by the generalized reflection and transmission method, in place of the transfer matrices. The associated generalized reflection and transmission coefficients are expressed by the ratios of Bessel or Hankel functions that obviate the notorious overflow problem for numerical computation. Finally, a set of linear matrix functions are constructed to solve for the EM waves in a borehole based on the concept of the generalized reflection, rather than that of the fictitious boundary. Numerical results in comparison with those from other approaches have demonstrated the validity and stability of our new formulations.

Volume Surface Integral Equation Method Based on Higher Order Hierarchical Vector Basis Functions for EM Scattering and Radiation From Composite Metallic and Dielectric Structures

This paper presents a novel Galerkin-type method of moments solution of the volume surface integral equation (VSIE), which is developed for the analysis of electromagnetic scattering and radiation from composite metallic and dielectric structures. Our new scheme utilizes curved tetrahedral elements and curved triangular patches for geometric modeling, and the associated higher order hierarchical vector (HOHV) basis functions for volume/surface current modeling. In contrast to the previous studies on higher order VSIE, our scheme, which is reported for the first time in VSIE, is much more flexible. In comparison with the conventional low-order scheme, our scheme requires much less memory and computational time for the same accuracy level. Numerical results are provided to demonstrate the accuracy, efficiency, and flexibility of our scheme.

Accurate Fracture Scattering Simulation by Thin Dielectric Sheet-Based Surface Integral Equation

The thin dielectric sheet-based surface integral equation (SIE) method is introduced to the accurate simulation of fracture scattering, which is an important and challenging topic in hydrocarbon exploration. In the proposed method, the equivalent volume current is decomposed into the equivalent surface current and the constant normal current. With this decomposition, the D-field volume integral equation degenerates into the SIE, which makes our proposed method stable, accurate, and efficient at low frequency. Numerical results have demonstrated its excellent performance.

A Hybrid Solver Based on Domain Decomposition Method for the Composite Scattering in Layered Medium

In the framework of domain decomposition method, we present a novel hybrid solver for accurate electromagnetic simulations of composite objects in layered medium (LM). This hybrid solver combines the surface integral equation method and the finite element method to effectively minimize the simulation domain, where the effect of inhomogeneous background is involved by the LM Greens functions, and the field transmission between neighboring subdomains is realized by the Riemann solver. Numerical results are given to validate the proposed solver.

A Stable Analytic Model for Tilted-Coil Antennas in a Concentrically Cylindrical Multilayered Anisotropic Medium

A set of compact and stable formulations is presented to calculate the response of logging tools employing tilted-coil antennas in anisotropic concentrically cylindrical multilayered formation. The presented formulations can be used to investigate the effect of mandrel, borehole, and invasion. Our formulations are different from previous ones in three aspects. First, the tool mandrel can be cylindrically multilayered, and electrical parameters of each layer are arbitrary. That is to say, the mandrel is not limited to being perfectly metallic. Second, the formation can be either anisotropic or isotropic. Finally, the propagation of electromagnetic wave in an inhomogeneous cylindrical medium is described by the generalized reflection and transmission coefficients without the numerical overflow issue. Numerical results in comparison with those from other approaches have demonstrated the validity and stability of our new formulations.

The influence of mesh fineness on virtual divergence factor for high frequency methods in electromagnetic scattering

Due to simplicity, high frequency hybrid methods based on ray tracing have been widely used for the fast simulations of electromagnetic scattering. For curved concave targets, the usage of faceted models might greatly degrade the accuracy of evaluation owing to the loss of divergence factor (DF). Recently, a new and efficient factor, entitled virtual divergence factor (VDF), has been proposed to play the role of DF. Although its validity and efficiency have been demonstrated convincingly, the influence of mesh fineness on VDF is still in need of study. In this paper, two composite targets of strong multiple ability, including a simplified model of “Ship on the Sea,” are analyzed. Based on the detailed comparisons of simulated results with different mesh sizes for the same target, it is found that in general the influence of mesh fineness is relatively small. This is highly desirable, and will make those ray tracing hybrid methods with VDF correction much more flexible and attractive.